The invention relates to a method for manufacturing a piezoelectric actuator employing a piezoelectric element which becomes deformed upon receipt of a supplied drive signal, and to a liquid ejecting head equipped with the actuator, as well as to an actuator mother member from which the piezoelectric actuator is originated.
A piezoelectric actuator is a member having a piezoelectric element which becomes deformed upon receipt of supplied electrical energy. The piezoelectric actuator is in widespread use as a drive element for, e.g., a liquid ejecting head, a micropump, and a sounding body (a speaker or the like). Here, the piezoelectric element is formed from piezoelectric ceramics made by compacting and sintering metal oxide powder, such as BaTiO3, PbZrO3, or PbTiO3, which are piezoelectric materials and exhibit a piezoelectric effect, or from a piezoelectric macromolecular film utilizing a high molecular compound.
Here, the liquid ejecting head ejects a droplet from a nozzle orifice by inducing pressure fluctuations in a liquid stored in a pressure chamber. The liquid ejecting head is embodied as, e.g., a recording head to be used in an image recording apparatus such as a printer, a liquid-crystal ejecting head for use in manufacturing a liquid-crystal display, or a coloring material ejecting head to be used for manufacturing a color filter. Here, the micropump is an ultrasmall pump capable of ejecting a very small volume of liquid and used at the time of, e.g., delivery of a trace amount of chemical.
The piezoelectric actuator is mounted on a pressure chamber formation substrate having a void which is to serve as a pressure chamber, and a portion of the pressure chamber is partitioned by the vibration plate. When ejection of a droplet or delivery of liquid is to be performed, a drive pulse is supplied to the piezoelectric element, to thereby deform the piezoelectric element and the vibration plate (i.e., the deformed portion of the pressure chamber) and vary the volume of the pressure chamber.
In the field of the liquid ejecting head and that of the micropump, strong demand exists for high-frequency driving of the piezoelectric element. This demand is intended for implementing high-frequency ejection of a droplet and enhancing liquid delivery capability. In order to implement high-frequency driving of the piezoelectric element, the compliance of the deformed portion must be made smaller than that of a related-art piezoelectric element and the extent to which the piezoelectric element is deformed must be made greater than that to which the related-art piezoelectric element is deformed. The reason for this is that a reduction in the compliance of the deformed portion results in enhancement of responsiveness, thereby enabling driving of the piezoelectric element at a frequency higher than that required conventionally. Another reason is that an increase in the extent to which the piezoelectric element is deformed results in an increase in volumetric change in the pressure chamber, and hence the volume of droplet to be ejected or the volume of droplet to be delivered can be increased.
A piezoelectric element of multilayer structure is proposed for sufficing for a characteristic pertaining to the compliance of the deformed portion and a characteristic pertaining to the extent to which the piezoelectric element becomes deformed, the characteristics being mutually contradictory. For example, a piezoelectric element disclosed in Japanese Patent Publication No. 2-289352A is formed from a piezoelectric layer having a two-layer structure; that is, an upper layer piezoelectric substance and a lower layer piezoelectric substance. Drive electrodes (individual electrodes) are formed at a boundary between the upper layer piezoelectric substance and the lower layer piezoelectric substance. A common electrode is formed on an outer surface of the upper layer piezoelectric substance, and another common electrode is formed on an outer surface of the lower layer piezoelectric substance. Similarly, Japanese Patent Publication No. 10-34924A discloses a piezoelectric element of multilayer structure.
In the case of the piezoelectric element of multilayer structure, the drive electrodes are provided at the boundary between the upper layer piezoelectric substance and the lower layer piezoelectric substance. Hence, an electric field, whose intensity is determined by an interval between the drive electrodes and the respective common electrodes (i.e., the thickness of each piezoelectric substance) and by a potential difference between the drive electrodes and the common electrodes, is imparted to the piezoelectric substances of respective layers. Therefore, in contrast with a piezoelectric element of monolayer structure formed by interposing a single layer piezoelectric substance between the common electrode and the drive electrodes, the piezoelectric element can be deformed at the same drive voltage as that conventionally required, even when the compliance of the deformed portion is reduced by increasing the total thickness of the piezoelectric element to some extent.
However, characteristics capable of responding to recently-growing demand cannot be achieved by mere use of the piezoelectric element of multilayer structure. Therefore, users are forced to use, as an actual product, a piezoelectric element of monolayer structure formed by interposing a single layer piezoelectric substance between a common electrode and drive electrodes. Various factors are conceivable as being responsible for this, including insufficient efficiency of deformation of the piezoelectric element.
For example, on the occasion of mass production of the piezoelectric actuator, manufacturing piezoelectric actuators on an individual basis deteriorates efficiency. Pressure chambers, piezoelectric elements, and feed terminals are provided in number equal to a plurality of units on a ceramic sheet, and the ceramic sheet is cut. When piezoelectric actuators are cut off from the ceramic sheet, electrode material may adhere to a cutting blade. When the electrode material has adhered to the cutting blade, sharpness of the cutting blade will be deteriorated, and there may arise a necessity for cleaning the electrode material adhering to the cutting blade, or a drop in manufacturing efficiency. Further, chips (cuttings) which have arisen during cutting of the ceramic sheet may cause a short-circuit.
The electrode materials adhere to the cutting blade because a feed terminal to be used for supplying an electric signal to the piezoelectric element is set to the maximum size. More specifically, on the occasion of fabricating the piezoelectric element, measurement of electrostatic capacitance is performed as a part of quality control operation, and the feed terminal is used for measuring electrostatic capacitance. In order to bring a probe of a measurement instrument into reliable contact with the feed terminal, the feed terminal must be made as large as possible. A portion of the feed terminal is formed so as to extend beyond a predetermined cutting line (i.e., a contour line of the piezoelectric actuator) provided on the ceramic sheet. Since the feed terminal is for feeding a drive signal to respective piezoelectric elements, the feed terminal remains conductive with a contact terminal of a wiring member; that is, remains electrically connected to the contact terminal. Therefore, when a configuration in which the feed terminal is to be cut is employed, the feed terminal is laid so as to extend up to the contour line of the piezoelectric actuator, thus ensuring electrical connection with the contact terminal. However, as mentioned previously, provision of the contact terminal in this manner is not preferable in terms of manufacturing efficiency.